Method of heating annular metallic bodies by electrical induction



Filed Oct. 10, 1960 June 1; 1965 E. BECKERT ETAL 3,187,155

METHOD OF HEATING ANNULAR METALLIC BODIES BY ELECTRICAL INDUCTION 3 Sheets-Sheet l June 1, 1965 E. BECKERT ETAL 3,187,155

METHOD OF HEATING ANNULAR METALLIC BODIES BY ELECTRICAL INDUCTION Filed 001$. 10, 1960 3 Sheets-Sheet 2 Fig. 3

Fig. 4

MAGNET'C AMPLIFIER \6 June 1, 1965 E. BECKERT ETAL 3,187,155

METHOD OF HEATING ANNULAR METALLIC BODIES BY ELECTRICAL INDUCTION Filed Oct. 10, 1960 5 SheetsSheet 3 MAGNETIC AMPLIFIERS MAGNETIC AMPLIFIER United States Patent 0 3,187,155 METHGD 0F HEATING ANNULAR METALLHQ BQEDIES BY ELECTRTCAL INDUCTEGN Ernst Becirert, Schweinfurt, and Wilhelm Viilhening, Dittelbrunn, near Schweinfurt, Germany, assignors to Kugelfischer Georg Schafer 8: (3a., @chweiufurt, Germany Filed Get. 10, 1960, Ser. No. 61,454 Claims priority, application Germany, Oct. 12, 1959, K 333% 1 Claim. '(Cl. 219-1055) The invention relates to a method of heating annular metallic bodies, particularly the race rings of antifriction bearings, by electrical inducton and of subsequently demagnetizing said bodies, whereby an adjustable supporting plate is used to support a plurality of annular bodies to be heated in such a manner that the said bodies encircle the respective one of the two limbs of the core of a transformer having a removable yoke member, the said bodies being so disposed above the primary winding of said transformer as to form the secondary winding thereof. 7

An annular body consisting of a magnetic metal such as antifriction bearing steel, when heated by electrical induction, will retain a greater or smaller amount of residual magnetism upon the induction current being cut oil. However, the antifriction bearing race rings are required to be non-magnetic when put to their contemplated use so as to prevent magnetic foreign material from lodging on the parts of the respective antifriction bearing, it being understood that such magnetic foreign material, when finding its way into the spaces between the rolling members of the bearings and the race members thereof, may give rise to damage to the said component parts. Therefore, it has already been proposed to provide for the antifriction bearing race rings, after the heating thereof by electrical induction, to be subjected to a separate operation in which they are demagnetized either by means of a demagnetizing plate or by means of a demagnetizing tunnel. Where this known method is adopted, each magnetized ring is passed through an alternating magnetic field whose strength decay toward zero. The said alternating magnetic field remains constant at its point of origin. The effective decay of the said field is the result of the ring to be demagnetized being moved from a region of maximum field strength in a region in which the intensity of the field practically equals zero. While this known method permits of the inductively heated rings being demagneti ed in a satisfactory manner, it has the drawback that it requires an additional operation as Well as a special device by means of which the additional operation is carried out.

In the case of the method of the present invention the said drawbacks are eliminated by providing for the primary voltage of the said transformer to be reduced, with the aid of an adjustable transformer, from the maximum exciting voltage to zero. In another embodiment of the invention, an electronic control system using electronic valves is used to reduce the primary voltage of the transformer from its maximum value to zero. In still another embodiment of the invention, similar results are obtained with the aid of a transducer. The improvement provided by the method according to the invention resides in the fact that the demagnetization of the said rings can be effected by means of the device used to heat the rings. This provides for considerable economies in comparison with conventional methods.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawing, illustrating preferred embodiments of the invention, wherein:

FIG. 1 is a diagrammatic representation of a device according to the invention which is adapted to heat annular bodies by means of electrical induction;

FIG. 2 is a chart illustrating the manner in which the magnetic flux used to demagnetize the said annular bodies is required to decay or decrease; and

FIGS. 3, 4 and 5 are wiring diagrams illustrating several embodiments of the method of the invention.

As will be seen from an inspection of FIG. 1, the annular bodies or rings 1 to be heated are placed on a vertically adjustable supporting plate 4 in such a manner that each ring encircles one of the two limbs of the core of a transformer 2, the said core comprising a removable yoke member 3, and the said rings being disposed above the primary winding 2:: of the transformer. Thus, the said rings, when in the positon indicated, will constitute the secondary winding of the transformer. The yoke member 3 of the core squarely abuts the adjacent ends of the two limbs of the core and is adapted to be raised and lowered by suitable mechanical, pneumatic or hydraulic means so as to permit the rings to be placed in position and to be removed upon completion of the operation. The heating device may be designed for operation on single-phase or multi-phase alternating current. In view of the mechanical gap existing between the primary windngs 2a of the transformer and the rings 1 to be heated, which rings constitute the secondary windings of the transformer, the primary and secondary windings are more or less closely coupled. The width of the said gap and hence the heating effect obtained may be varied by moving the supporting plate 4 towards or away from the primary winding 2a as indicated in PEG. 1 by the double-headed arrow.

The reduction in intensity of the magnetic flux illustrated in FIG. 2 and required for the demagnetization of the rings is effected in the case of the embodiment shown in FIG. 3 by reducing the primary voltage in the windings 2a of the transformer 2b from the maximum value of the exciting voltage to zero, this being done by means of an adjustable transformer 5 which may, for example, be driven by a suitable motor.

in the case of another embodiment of the invention (not shown), similar results can be achieved by the use of a control system using electronic valves.

FIG. 4 illustrates another embodiment in which use is made of a transducer 6 for the purpose of gradually reducing the exciting voltage applied to the primary winding of the transformer. Upon the current supply to control the transducer being interrupted, the inherent time constant of the transducer will cause a continuous decay towards zero of the voltage applied to the primary winding of the transformer. The said time constant may be increased by inserting an RC network into the control circuit. The yoke member 3a is raised immediately upon completion of the heating and demagnetizing operation. In order to ensure that the demagnetizing operation has brought about the desired effect, a voltage monitoring relay 7 is connected to the terminals of the primary winding of the transformer, the said relay being adapted not to release the yoke member 3a until the primary voltage has for practical purposes been reduced to zero, for example to 2 percent of the rated voltage.

MG. 5 shows the wiring diagram of a practical embodiment of a device according to the invention using electrical induction for heating purposes and transducercontrolled demagnetizing means. The heating circuit proper is designed for operation on three-phase current. The three main transducers 8a, 3b, 8c are controlled by a a primary transducer 9. The control cirucit 1 includes an ammeter A which may be calibrated, for example, in terms of percent power output, since the heating power is 'a function of the control current. The desired heating power can be selected by adjusting a potentiometer to vary the control current 2 for the primary transducer 9. The voltage monitoring relay 10 mentioned earlier also comprises a transducer 11 and, upon the actual voltage reaching a value of 2 percent of the rated voltage, will produce a signal initiating the raising of the yoke member described earlier. The desired heating period can be selected by adjusting a time delay relayZ.

What is claimed is:

An apparatus for heating inductively metal rings by electrical means and for subsequently eliminating residual magnetism comprising a transformer-type core enclosing at least two limbs, a first and a second yoke connecting neighboring ends of said limbs, said second yoke being detachable in order to place a ring over at least one of said limbs, at least one primary winding on at least one of said limbs, a first source of alternating exciting voltage, magnetic amplifier means with an inherent time constant,'said amplifier means including a first amplifying branch and a second control branch, said primary winding being connected to said first source, said first branch of said magnetic amplifier means being interconnected between said source and said primary, said second control branch being provided with an RC- network to adjust said time constant or" said amplifier means, a second source of direct control voltage con nected to said second control branch of said amplifier means,'means to interrupt the connection between said second source of voltage and said second control branch in order to reduce the influence of said exciting voltage of said first source on said primary steadily to at least substantially zero due to the time constant of said amplifier means, and a relay, said relay being connected in parallel to said primary and adapted to change its position when'the voltage of said primary has dropped to about two percent of its maximum value, said change of said position effecting a release of said second detachable yoke.

References Cited by theExaminer UNITED STATES PATENTS 458,163 8/91 Gutmann 21910.75 1,234,280 7/17 Burnett et a1 2l910.75 X 1,987,458 1/35 Adams 219-10.7'5 2,445,459 7/48 Snyder 317157.5 2,786,970 '3/57 Connoy 317--157.5 2,975,239 3/61 Jackson et al 317-1575 3,049,208 8/62 Parkes 3l7-157.61 3,078,396 2/63 Engelsted 3l7157.5

RICHARD M. 'WOOD, Primary Examiner.

MAX L. LEVY, Examiner, 

